During recent years an increasing demand for detecting characteristics of aerosols has arisen. One of the more delicate issues in determining the characteristics of aerosols is determination of the weight of nano-sized particles due to inter alia the inherent small dimensions.
In a work presented by the inventors in Real-Time Particle Mass Spectrometry Based on Resonant Micro Strings, Sensors 2010, 10, 8092-8100 it has been shown that the weight of micro-sized particles arranged on a micro string by hand can be determined from the resonance frequency of the micro string. Further, Naik et. al. in Towards single-molecule nanomechanical mass spectrometry, DOI: 10.1039 disclose a system to determining weight of nano-sized particles where particles are delivered to a detector in vaccum by hexapole ion optics. However, such manual arrangement of nano-sized particles on micro strings or utilising vacuum in combination with ion optics appear impractical.
U.S. Pat. No. 5,572,322 discloses an apparatus that measures the diameter, relative concentration and weight of particles. The detection of scattered light produced when light is projected at particles drawn into a nozzle-shaped measuring space is used to measure particle diameter. Particle concentration is measured based-on variations in the intensity of transmitted light, and particle weight is measured based on changes in operating frequency of a crystal oscillator resulting from the adhesion of particles on the surface of the crystal oscillator.
However, the system according to U.S. Pat. No. 5,572,322 is prone to in-accurate measurements of the particle weight as the deflection of the aerosol and thereby also the particles will result in that lighter particles escapes deposition on the surface of the crystal oscillator and only the heavier ones will deposit on the surface of the crystal oscillator.
WO2008/020903 disclose a method for detection of airborne biological agent using a self-exciting, self-sensing piezoelectric sensor that includes a piezoelectric layer and a non-piezoelectric layer. A recognition entity is placed on one or both layers. The antibody that recognizes and binds to the airborne species may be chemically immobilized on the cantilever sensor surface. Further, an analyte attractor is applied to the non-piezoelectric portion of the sensor, the attractor being specific to an analyte. Thus, the deposition of substance on the sensor according to WO2008/020903 is limited to know, specific substances which is attracted to the surface of a recessed sensor and the sensor is not applicable to determine the weight of e.g. unknown airborne substances.
Thus, while different measurement techniques are suggested to measure the weight of nano sized particles, they still suffer from the drawback of measuring in a practical manner the weight of representative, i.e. not only heavier ones, nano-sized particles.
Hence, an improved device and method for determining the weight of nano-sized particles of an aerosol would be advantageous, and in particular a more efficient and/or reliable device and method for determining such weights would be advantageous.